This invention relates to ultrasonic inspection of articles and, more particularly, to the improved blind inspection of a member within an assembled article through an access port, for example the inspection of a gas turbine engine rotor through a borescope opening while the rotor is assembled in the engine.
The primary power source for present aircraft is the gas turbine engine. Also, a variety of land-based or marine applications of such power producing apparatus has been developed. Among the technology advances in such an art has been the significant increase in safe operating life of individual members or components assembled into such an engine. Nevertheless, earlier inspection of such members sometimes becomes desirable and informative.
In order to provide limited observation of components within a gas turbine engine while the engine is still assembled, access ports have been designed in the walls of members, such as casings, to provide for the borescopic, optical inspection of internal members. One such inspection device and method is shown in U.S. Pat. No. 3,778,170--Howell et al, issued Dec. 11, 1973, the disclosure of which is incorporated herein by reference.
The ultrasonic inspection technique, to which the present invention more particularly relates, is a well known and highly developed art. In general, it involves sending an electrical impulse to a transducer which converts the impulse into ultrasonic frequency mechanical vibrations and transmits such vibrations through a liquid couplant such as water, glycerine or an oil, to an article. Such a signal will be reflected by any surface it encounters on or in the article. Electrical analysis apparatus or instruments are commercially available to assist in the identification of any reflected signal for the determination of defects, including flaws and discontinuities, within the article member being inspected. As used in this specification, the term "defects" is intended to include any such condition predetermined to be undesirable within an article. As a nondestructive testing or inspection means, ultrasonic techniques have been found to be useful in determining the quality of a variety of articles in which internal defects can occur during their manufacture.
During use of ultrasonic inspection, it is required that the transducer be properly positioned with respect to the surface of a member which is being inspected. Therefore, the use of such an inspection technique within an assembled article, for the fluid inspection of a member portion difficult to reach by normal methods, has presented difficult positioning and alignment problems. In addition, the inaccessibility of portions of a member to be inspected has precluded the direct transmission of an ultrasonic signal toward the protion.